2gar

A PH-DEPENDENT STABLIZATION OF AN ACTIVE SITE LOOP OBSERVED FROM LOW AND HIGH PH CRYSTAL STRUCTURES OF MUTANT MONOMERIC GLYCINAMIDE RIBONUCLEOTIDE TRANSFORMYLASE

spinqualitylabelsall models 2gar, resolution 1.80Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 2gar is a 1 chain structure with sequence from Escherichia coli. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 1.8Å Ligands: PO4 Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function PUR3_ECOLI Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed A mutation in the dimer interface of Escherichia coli glycinamide ribonucleotide transformylase (GarTfase) disrupts the observed pH-dependent association of the wild-type enzyme, but has no observable effect on the enzyme activity. Here, we assess whether a pH effect on the enzyme's conformation is sufficient by itself to explain the pH-dependence of the GarTfase reaction. A pH-dependent conformational change is observed between two high-resolution crystal structures of the Glu70Ala mutant GarTfase at pH 3.5 (1.8 A) and 7.5 (1.9 A). Residues 110 to 131 in GarTfase undergo a transformation from a disordered loop at pH 3.5, where the enzyme is inactive, to an ordered loop-helix structure at pH 7.5, where the enzyme is active. The ordering of this flexible loop-helix has a direct effect on catalytic residues in the active site, binding of the folate cofactor and shielding of the active site from solvent. A main-chain carbonyl oxygen atom from Tyr115 in the ordered loop forms a hydrogen bond with His108, and thereby provides electronic and structural stabilization of this key active site residue. Kinetic data indicate that the pKa of His108 is in fact raised to 9. 2. The loop movement can be correlated with elevation of the His pKa, but with further stabilization, probably from Asp144, after the binding of folate cofactor. Leu118, also in the loop, becomes positioned near the p-amino benzoic acid binding site, providing additional hydrophobic interactions with the cofactor 10-formyl tetrahydrofolate. Thus, the pH-dependence of the enzyme activity appears to arise from local active site rearrangements and not from differences due to monomer-dimer association. A pH-dependent stabilization of an active site loop observed from low and high pH crystal structures of mutant monomeric glycinamide ribonucleotide transformylase at 1.8 to 1.9 A.,Su Y, Yamashita MM, Greasley SE, Mullen CA, Shim JH, Jennings PA, Benkovic SJ, Wilson IA J Mol Biol. 1998 Aug 21;281(3):485-99. PMID:9698564 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.

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